The invention relates generally to semiconductor device fabrication and, in particular, to system, methods, and computer program products for evaluating the time-dependent dielectric breakdown of a dielectric layer in a semiconductor device, such as the gate dielectric layer of a metal-oxide-semiconductor field-effect transistor (MOSFET).
Time-dependent dielectric breakdown (TDDB) is a progressive failure mechanism observed in semiconductor devices, such as metal-oxide-semiconductor field-effect transistors. TDDB occurs over time and may eventually cause the gate dielectric layer to break down from the extended application of a voltage during operation. When a MOSFET is operated for lengthy periods at normal supply voltages, the gate leakage current increases gradually as defects are accumulated in the gate dielectric layer. This process ultimately leads to device breakdown as TDDB may eventually form a conducting path through the gate oxide to the substrate. Essentially, the electrical insulating properties of the gate dielectric layer may be lost, which causes the gate and the channel region to become electrically shorted and leads to the failure of the MOSFET.
Reliability tests are routinely used to estimate an expected lifetime of a gate dielectric layer so that device performance can be guaranteed to remain within the device's specification for a determined period of time. Under operating conditions with normal supply voltages biasing the gate, reliability testing would take an impractically long period of time. Consequently, reliability testing is usually performed by applying excess electrical stress in the form of voltage and/or current on the gate dielectric layer. The stress promotes the faster accumulation of defects, which accelerates the breakdown of the gate dielectric layer. The breakdown may be further accelerated by testing at elevated temperatures. The lifetime of a gate dielectric layer under operating conditions can then be determined from an extrapolation of the results of reliability testing.
Improved methods of reliability testing, apparatus for reliability testing, and computer program products are needed.